U.S. patent application number 11/009073 was filed with the patent office on 2005-06-30 for ink jet printing apparatus, ink jet printing method and print head.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Karita, Seiichiro, Ogino, Hiroyuki, Shibata, Tsuyoshi.
Application Number | 20050140722 11/009073 |
Document ID | / |
Family ID | 34703274 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050140722 |
Kind Code |
A1 |
Shibata, Tsuyoshi ; et
al. |
June 30, 2005 |
Ink jet printing apparatus, ink jet printing method and print
head
Abstract
An ink jet print head is provided which can print a high-quality
image with no density variation-caused lines at high speed and
which can be manufactured at low cost and with ease. For this
purpose, the print head of this invention has a plurality of nozzle
groups each having at least one nozzle array arranged in a
predetermined array direction Y crossing a relative motion
direction X. A distance in the relative motion direction between
the nozzles in each nozzle group adjoining each other in the array
direction Y is set almost equal to a distance in the relative
motion direction between the nozzle groups adjoining each other in
the array direction Y.
Inventors: |
Shibata, Tsuyoshi;
(Yokohama-shi, JP) ; Karita, Seiichiro; (Toda-shi,
JP) ; Ogino, Hiroyuki; (Yokohama-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
34703274 |
Appl. No.: |
11/009073 |
Filed: |
December 13, 2004 |
Current U.S.
Class: |
347/40 |
Current CPC
Class: |
B41J 2/15 20130101; B41J
2/155 20130101; B41J 2202/20 20130101; B41J 2/515 20130101 |
Class at
Publication: |
347/040 |
International
Class: |
B41J 002/145; B41J
002/15 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2003 |
JP |
2003-417361 |
Oct 22, 2004 |
JP |
2004-308822 |
Claims
What is claimed is:
1. An ink Jet printing apparatus for forming an image on a print
medium by moving a print head having a plurality of ink ejection
nozzles relative to the print medium as the print head ejects ink
from the nozzles during a printing operation; wherein the print
head comprises a plurality of nozzle groups each having at least
one nozzle array arranged in a predetermined array direction
crossing the print head-print medium relative motion direction;
wherein a distance in the relative motion direction between the
nozzles adjoining each other in the array direction in each nozzle
group is set almost equal to a distance in the relative motion
direction between the nozzle groups adjoining each other in the
array direction.
2. An ink jet printing apparatus for forming an image on a print
medium by moving a print head having a plurality of ink ejection
nozzles relative to the print medium as the print head ejects ink
from the nozzles during a printing operation; wherein the print
head comprises a plurality of nozzle groups each having a plurality
of nozzle arrays arranged side by side, each of the nozzle arrays
having a plurality of nozzles arranged in a predetermined array
direction crossing the print head-print medium relative motion
direction; wherein the nozzles in each nozzle array in each nozzle
group are arranged in positions different in the array direction
and in the relative motion direction from those of the nozzles in
other nozzle arrays so that the nozzles in each nozzle group are
arranged in a staggered pattern; wherein the plurality of nozzle
groups are arranged in positions differing from each other in the
array direction and in the relative motion direction so that they
are arranged in a staggered pattern in the print head; wherein a
distance in the relative motion direction between the nozzles
adjoining each other in the array direction in each nozzle group is
set almost equal to a distance in the relative motion direction
between the nozzle groups adjoining each other in the array
direction.
3. An ink jet printing apparatus according to claim 1, wherein the
adjoining nozzles in each nozzle array are arranged in positions
differing from each other in the relative motion direction and in
the array direction so that they are arranged in a staggered
pattern.
4. An ink jet printing apparatus according to claim 2, wherein the
adjoining nozzles in each nozzle array are arranged in positions
differing from each other in the relative motion direction and in
the array direction so that they are arranged in a staggered
pattern.
5. An ink jet printing apparatus according to any one of claim 1 to
4, wherein each nozzle array is made up of a line of nozzles.
6. An ink jet printing apparatus according to any one of claim 1 to
4, wherein at least two nozzle groups adjoining each other in the
array direction are arranged in positions such that the nozzle
arrays in one nozzle group partly overlap at one end the nozzle
arrays in the other nozzle group.
7. An ink jet printing apparatus according to claim 5, wherein at
least two nozzle groups adjoining each other in the array direction
are arranged in positions such that the nozzle arrays in one nozzle
group partly overlap at one end the nozzle arrays in the other
nozzle group.
8. An ink jet printing method for forming an image on a print
medium by moving a print head having a plurality of ink ejection
nozzles relative to the print medium as the print head ejects ink
from the nozzles during a printing operation; wherein the print
head has a plurality of nozzles arranged at a constant pitch in a
predetermined array direction crossing the print head-print medium
relative motion direction; wherein distances in the relative motion
direction between the nozzles adjoining each other in the array
direction are set almost equal; wherein the print head is moved at
a constant scan speed so that ink dots adjoining each other in the
array direction are formed at an almost constant time interval.
9. An ink jet printing method for forming an image on a print
medium by moving a print head having a plurality of ink ejection
nozzles relative to the print medium as the print head ejects ink
from the nozzles during a printing operation; wherein the print
head comprises a plurality of nozzle groups each having a plurality
of nozzle arrays arranged side by side, each of the nozzle arrays
having a plurality of nozzles arranged in a predetermined array
direction crossing the print head-print medium relative motion
direction; wherein the nozzles in each nozzle array in each nozzle
group are arranged in positions different in the array direction
and in the relative motion direction from those of the nozzles in
other nozzle arrays so that the nozzles in each nozzle group are
arranged in a staggered pattern; wherein the plurality of nozzle
groups are arranged in positions differing from each other in the
array direction and in the relative motion direction so that they
are arranged in a staggered pattern in the print head; wherein a
distance in the relative motion direction between the nozzles
adjoining each other in the array direction in each nozzle group is
set almost equal to a distance in the relative motion direction
between the nozzle groups adjoining each other in the array
direction; wherein the print head is moved at a constant scan speed
so that ink dots adjoining each other in the array direction are
formed at an almost constant time interval.
10. A print head having a plurality of ink ejection nozzles,
comprising: a plurality of nozzle groups each having at least one
nozzle array arranged in a predetermined array direction crossing a
relative motion direction, the relative motion direction being a
direction in which the print head is moved relative to a print
medium during a printing operation; wherein a distance in the
relative motion direction between the nozzles adjoining each other
in the array direction in each nozzle group is set almost equal to
a distance in the relative motion direction between the nozzle
groups adjoining each other in the array direction.
11. A print head having a plurality of ink ejection nozzles,
comprising: a plurality of nozzle groups each having a plurality of
nozzle arrays arranged side by side, each of the nozzle arrays
having a plurality of nozzles arranged in a predetermined array
direction crossing a relative motion direction, the relative motion
direction being a direction in which the print head is moved
relative to a print medium during a printing operation; wherein the
nozzles in each nozzle array in each nozzle group are arranged in
positions different in the array direction and in the relative
motion direction from those of the nozzles in other nozzle arrays
so that the nozzles in each nozzle group are arranged in a
staggered pattern; wherein the plurality of nozzle groups are
arranged in positions differing from each other in the array
direction and in the relative motion direction so that they are
arranged in a staggered pattern in the print head; wherein a
distance in the relative motion direction between the nozzles
adjoining each other in the array direction in each nozzle group is
set almost equal to a distance in the relative motion direction
between the nozzle groups adjoining each other in the array
direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an Ink jet print head
having nozzles densely arrayed therein to eject ink containing a
colorant, and to an ink jet printing apparatus and an ink jet
printing method to form an image using the print head. More
specifically, the present invention relates to an ink jet printing
apparatus and an ink jet printing method using an elongate print
head which has a plurality of nozzle groups each made up of a array
of nozzles arranged staggered between two parallel lines, one on an
upstream side and the other on a downstream side with respect to a
direction in which a print medium is moved relative to the print
head. Particularly, this invention relates to an ink jet printing
method, an ink jet printing apparatus and a print head suited for a
so-called one-pass printing in which the elongate print head Is
scanned only once over a print area to complete a printed
image.
[0003] This invention is applicable to all devices that print on
print mediums made of paper, cloth, nonwoven fabric, OHP sheets and
metal materials. Examples of applicable devices include office
equipment such as printers, copying machines and facsimiles, and
industrial manufacturing equipment.
[0004] 2. Description of the Related Art
[0005] As information processing equipment, such as copying
machines, word processors and computers, and communication
equipment make technological advances, ink jet printing apparatus
that print digital images by an ink jet method are becoming
increasingly widespread as an image recording device for these
equipment. One of the ink jet printing apparatus is known to use a
print head that has a plurality of print elements (also referred to
as nozzles) densely arrayed therein to increase a print speed.
Further, in recent years there is a growing demand for a capability
to print color images and, in response to this demand, printing
apparatus that use a plurality of print heads for ejecting color
inks are in common use. What is meant by a nozzle as referred to in
this specification and the scope of claim is one that includes an
ink ejection opening to eject ink supplied into a common ink
chamber in the print head, an ink path to introduce ink supplied
into the common ink chamber to the ink ejection opening, and an
ejection energy generation element to eject ink supplied to the ink
path from the ink ejection opening.
[0006] Generally, an ink jet printing apparatus ejects ink or
recording liquid in the form of flying ink droplets onto a variety
of print mediums made of such material as paper to form an image
thereon. Since the ink jet printing apparatus adopts a non-contact
system by which the print head does not contact the print medium,
the printing can be performed with low noise. Another advantage is
that the print resolution and the print speed can be increased by
increasing the nozzle density. Further, the ink jet printing
apparatus does not need special processing, such as development and
fixing, even for such print mediums as plain paper. All these
advantages allow for the printing of images at low cost and at high
quality and therefore the ink jet printing apparatus is finding an
ever widening range of applications. An on-demand type ink jet
printing apparatus in particular has the advantages of being able
to be easily upgraded to print color images and be reduced in size
and simplified in construction and thus its demand is expected to
expand in the future. As a demand for a capability to print color
images grows, so does the need for higher print quality and faster
print speed.
[0007] With a remarkable advance in recent years in the technology
to form nozzles with high density, a fabrication of a high-density,
elongate print head has come to be realized. An elongate print head
having nozzles arrayed at high density is generally called a
full-multi type elongate print head An ink jet printing apparatus
using such an elongate print head has been proposed and implemented
which completes a printed image in one printing scan over a wide
print area corresponding to the elongate print head. This ink jet
printing apparatus can meet requirements for both print speed and
print quality. Because of these advantages, further efforts for
development are being made on this type of printing apparatus.
[0008] However, the ink jet printing apparatus using the elongate
print head with high-density nozzles has the following
problems.
[0009] First, in the above system if an image in a print area is to
be completed in one printing scan (one pass) or in a small number
of passes, ink droplets ejected from the nozzles of print head
units need to be absorbed and fixed in the print medium in a short
period of time. This requires a bulky heat and dry means for the
print medium or a means to reduce a volume of ink used for
printing. This in turn increases cost and reduces the print density
or pixel density, degrading the quality of the printed image.
[0010] Second, if the nozzles are arrayed at high density in a
single line, ink droplets ejected from the adjoining nozzles may
merge together on the print medium into an inappropriate shape.
When an image to be printed has a high duty, the ink that failed to
be absorbed in the print medium may remain on the print medium in a
liquid state, degrading the print quality.
[0011] Third, ink dots formed by those nozzles in a boundary
portion between the nozzle groups may produce artifacts such as
streaking caused by optical density variations which shows up in
the form of white or black lines, degrading a print quality.
[0012] To avoid this problem, a print head has been proposed which
has nozzle groups each having two parallel lines of nozzles, one on
an upstream side and one on a downstream side, so that the nozzles
are staggered alternately between the upstream and downstream
parallel lines. Further, in this configuration, the nozzle groups
are connected longitudinally to form an elongate head for use in a
full-line printer.
[0013] In an ink jet printing apparatus using the above print head
having a plurality of longitudinally connected nozzle groups,
however, a problem has been observed. Although white or black lines
are rendered less conspicuous in an image area printed by those
nozzles in one nozzle group, an image area printed by those nozzles
in the boundary portion between the nozzle groups may still show
white or black lines. A satisfactory image quality has yet to be
obtained with this type of ink jet printing apparatus.
SUMMARY OF THE INVENTION
[0014] An object of this invention is to provide an elongate print
head which can print a high-quality image with no density
variation-caused lines at high speed and which can be manufactured
at low cost and with ease and to provide an ink jet printing
apparatus and an ink jet printing method using this print head.
[0015] Another object of this invention is to provide an ink jet
printing apparatus for forming an image on a print medium by moving
a print head having a plurality of ink ejection nozzles relative to
the print medium as the print head ejects ink from the nozzles
during a printing operation; wherein the print head comprises a
plurality of nozzle groups each having at least one nozzle array
arranged in a predetermined array direction crossing the print
head-print medium relative motion direction; wherein a distance in
the relative motion direction between the nozzles adjoining each
other in the array direction in each nozzle group is set almost
equal to a distance in the relative motion direction between the
nozzle groups adjoining each other in the array direction.
[0016] A still another object of this invention is to provide a
print head having a plurality of ink ejection nozzles, comprising:
a plurality of nozzle groups each having at least one nozzle array
arranged in a predetermined array direction crossing a relative
motion direction, the relative motion direction being a direction
in which the print head is moved relative to a print medium during
a printing operation; wherein a distance in the relative motion
direction between the nozzles adjoining each other in the array
direction in each nozzle group is set almost equal to a distance in
the relative motion direction between the nozzle groups adjoining
each other in the array direction.
[0017] The above and other objects, effects, features and
advantages of the present invention will become more apparent from
the following description of embodiments thereof taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic view showing a conceptual construction
of an ink jet printing apparatus applied to an embodiment of this
invention;
[0019] FIG. 2 is a plan view schematically showing an arrangement
of print heads;
[0020] FIG. 3 Is an exploded perspective view showing an inner
construction of the print head of this invention;
[0021] FIG. 4 is a block diagram showing an example configuration
of a control system in the ink jet printing apparatus of this
invention;
[0022] FIG. 5A is a schematic diagram showing a nozzle array in an
elongate print head according to the related technology of this
invention;
[0023] FIG. 5B illustrates an image printed using the print head of
FIG. 5A;
[0024] FIG. 6 is a schematic diagram showing another nozzle array
in the elongate print head according to the related technology of
this invention;
[0025] FIG. 7 is a schematic diagram showing still another nozzle
array in the elongate print head according to the related
technology of this invention;
[0026] FIG. 8 is a schematic diagram showing yet another nozzle
array in the elongate print head according to the related
technology of this invention;
[0027] FIG. 9 is a schematic diagram showing a nozzle array of an
elongate print head in a first embodiment of this invention;
[0028] FIG. 10 is a schematic diagram showing a nozzle array of an
elongate print head in a second embodiment of this invention;
[0029] FIG. 11 is a schematic diagram showing a nozzle array of an
elongate print head in a third embodiment of this invention;
[0030] FIG. 12 is a schematic diagram showing a nozzle array of an
elongate print head in a forth embodiment of this invention;
and
[0031] FIG. 13A, FIG. 13B and FIG. 13C are schematic diagrams
showing how a merged dot is formed of two ink droplets ejected from
two adjoining nozzles of the print head.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0032] Now, preferred embodiments of this invention will be
described in detail by referring to the accompanying drawings.
[0033] FIG. 1 is a schematic diagram showing a conceptual
construction of an ink jet printing apparatus applied to
embodiments of this invention. FIG. 2 is a plan view schematically
showing an arrangement of print heads.
[0034] An ink jet printing apparatus 1 of this embodiment is a
color ink jet printing apparatus having a plurality of parallelly
arranged elongate print heads 2Y, 2M, 2C, 2BK extending in a
direction perpendicular to a direction of feed of a print medium.
Denoted 2Y is a print head to eject a yellow ink, 2M a print head
to eject a magenta ink, 2C a print head to eject a cyan ink, and
2Bk a print head to eject a black ink. These print heads have
almost the same construction and thus, unless otherwise
specifically stated, they are generally described as a print head
2.
[0035] These print heads 2 are connected to four ink tanks 3Y, 3M,
3C, 3Bk (hereinafter referred to generally as an ink tank 3)
containing yellow, magenta, cyan and black inks, respectively,
through connecting tubes 4. These ink tanks 3 are removable from
the connecting tubes 4 for replacement.
[0036] The print heads 2 can be moved vertically toward and away
from a platen 6 by a head moving means 10 dedicated for recovery
processing that is controlled by a controller 9. The print heads 2
are arranged at a predetermined interval in a transport direction
of an endless transport belt 5 in such a way that they face the
platen 6 with the transport belt 5 interposed therebetween. The
print head 2 is formed with ink ejection openings, a common ink
chamber to which an ink is supplied from the ink tank 3, and ink
paths for introducing the ink from the common ink chamber to
individual ink ejection openings. In each ink path there is
provided a nozzle that has an electrothermal transducer (heater) as
an ejection energy generation means to generate thermal energy for
ejecting the ink supplied. The heaters are electrically connected
to a controller 9 through a head driver 2a. The energizing and
de-energizing of the heaters is controlled according to an on/off
signal (ejection/non-ejection signal) sent from the controller.
[0037] By the side of each print head 2 head caps 7 are arranged at
the same intervals as, but shifted half a pitch from, the print
heads to discharge viscous ink from the ink paths prior to
performing a printing operation on a print medium P to recover an
ejection performance of the print heads. The head caps 7 can be
moved to directly under the print heads 2 by a cap moving means 8
controlled by the controller 9 to receive waste ink discharged form
the ink ejection openings.
[0038] The transport belt 5 for feeding the print medium P is wound
around drive rollers connected to a belt drive motor 11, which is
driven by a motor driver 12 connected to the controller 9. Upstream
of the transport belt 5 is installed a charger 13 that charges the
transport belt 5 to bring the print medium P into intimate contact
with the transport belt 5. The charger 13 is energized/de-energized
by a charger driver 13a connected to the controller 9. A pair of
feed rollers 14, 14 to feed the print medium P onto the transport
belt 5 is connected to a feed motor 15 that drives the feed rollers
14, 14. The feed motor 15 is operated by a motor driver 16
connected to the controller 9.
[0039] In performing a printing operation on the print medium P,
the print heads 2 are first lifted away from the platen 6. Next,
the head caps 7 are moved to directly under the individual print
heads 2 to perform the recovery operation and then returned to the
standby position. After this, the print heads 2 are lowered toward
the platen until they reach the print position. Then, the charger
13 is energized, and at the same time the transport belt 5 is
driven, the print medium P is fed by the feed rollers 14, 14 onto
the transport belt, and the print heads 2 are activated to form a
color image on the print medium P.
[0040] Next, referring to FIG. 3, the inner construction of the
print head 2 will be described.
[0041] In the figure, the ink jet print head 2 has a heater board
23 formed with a plurality of heaters 22 for heating ink and a top
plate 24 mounted on the heater board 23. The top plate 24 is formed
with a plurality of ink ejection openings 25. Behind each of the
ink ejection openings 25 a tunnel-like ink path 26 is formed which
communicates with the corresponding ink ejection opening 25. The
ink paths 26 are commonly connected at their rear end to an ink
chamber. The ink chamber is supplied an ink from the associated ink
tank 3. The ink supplied to the ink chamber is then fed to
individual ink paths 26.
[0042] The heater board 23 and the top plate 24 are assembled so
that the heaters 22 align with the corresponding ink paths 26. The
heaters 22, although only four of them are shown in FIG. 3, are
assigned one to each ink path 26. In the assembled print head, when
a predetermined drive pulse is applied to the heaters 22, ink over
each heater 22 boils to produce a bubble which, as its volume
expands, expels an ink droplet from the ink ejection opening 25.
The ink jet printing system applicable to this invention is not
limited to a so-called bubble jet (registered tradename) system
that uses the heaters as shown in FIG. 1 and FIG. 2. For example,
in the case of a continuous system that continuously ejects ink for
drop formation, a charge control type and a diffusion control type
may be applied. In the case of an on-demand system that ejects ink
droplets on demand, a pressure control type that ejects ink drops
from ink ejection openings by mechanical vibrations produced by a
piezoelectric oscillation device can be applied.
[0043] FIG. 4 is a block diagram showing an example configuration
of a control system in the ink jet printing apparatus of this
invention.
[0044] In FIG. 4, denoted 31 is an image data input unit to enter
multi-valued image data from image input devices such as scanner
and digital camera and multi-valued image data stored in a hard
disk of a personal computer, 32 an operation unit having a variety
of keys to set parameters and instruct a start of printing, and 33
a CPU as a control means to control the entire printing apparatus
according to various programs in storage media. Reference number 34
represents a storage means for storing a variety of data. The
storage means 34 has a print medium information storage area 34a to
store information about the kind of print medium, an ink
information storage area 34b to store information about ink used
for printing, an environment information storage area 34c to store
information on the environment at time of printing such as
temperature and humidity, and a control program group storage area
34d. A RAM 35 is used as a work area for various programs in the
storage means 34, as a temporary save area for processing errors,
and as a work area for processing an image. In this embodiment all
operations are performed according to the programs in the storage
means. As the storage means 34 to store the programs, ROM, FD,
CD-ROM, HD, memory card and magnetooptical disc may be used. The
RAM 35 may also be used to copy various tables in the storage means
34 and then change the contents of the tables so that the image
processing can be performed by referring to the modified
tables.
[0045] Denoted 36 is an image data processing unit which quantizes
input multi-valued image data into N-valued image data for each
pixel and generates an ejection pattern according to Quantized
grayscale values "K" of individual pixels. The image data
processing unit 36 transforms input multi-valued image data into
N-valued image data and then creates an ejection pattern that
matches the grayscale values "K". For example, if 8-bit
multi-valued image data (representing 256 grayscale levels) is
supplied to the image data input unit 31, the image data processing
unit 36 transforms grayscale values of the image data to be output
into K values. While a multi-value error diffusion method is used
in the process of transforming input grayscale image data to K
values in this example, any desired half-tone processing method,
such as average density storage method and dither matrix method,
may be employed. Based on image density information, the
transform-to-K-value processing is repeated for all pixels to
generate binary drive signals dictating whether individual nozzles
are to eject or not eject ink for each pixel.
[0046] Denoted 37 is an image printing unit 37 to eject ink
according to the ejection pattern generated by the image data
processing unit 36 to form a dot image on a print medium.
Designated 38 is a bus line to transfer an address signal, data and
control signal in the printing apparatus.
[0047] Next, referring to FIGS. 5A and 5B, FIG. 6 to FIG. 12, and
FIGS. 13A to 13C, a nozzle arrangement in the print head, the
feature of this invention, will be described. To clarify the
feature of preferred embodiments of this invention, let us first
describe a technology related to this invention and then explain
the nozzle arrangement and the print head arrangement in the
embodiments, focusing on differences between this invention and its
related technology
[0048] (Related Technology)
[0049] FIG. 5A shows an elongate print head used for a full-line
type ink jet print head and FIG. 5B illustrates an image printed by
the print head of FIG. 5A.
[0050] In FIG. 5A, denoted 41 to 44 are head nozzle groups each
having 512 nozzles arranged in two left and right arrays staggered
from each other. These nozzle groups 41 to 44 are arranged
staggered on left and right side alternately so that they
collectively form an elongate print head 45. While the elongate
print head 45 of FIG. 5A is shown to have a total of 2048 nozzles
by connecting the four nozzle groups 41-44, it is possible to have
three or four or more nozzle groups connected in one print
head.
[0051] Here, how an image is formed by an ink jet printing
apparatus using the elongate print head 45 will be described. The
print data to be printed by the print head 45 is generated by
separating an input Image into individual colors for the
corresponding heads and binarizing the color-separated gray image
by the error diffusion method.
[0052] When a gray image, such as shown in FIG. 5B, is printed by
the elongate print head 45, ink droplets from adjoining nozzles in
each of the nozzle groups 41, 43 are ejected almost simultaneously
and land on a print medium almost simultaneously to form printed
regions 48A, 48C, although this process is somewhat affected by the
ink ejection volume, the kind of ink and print medium and the print
speed. A time duration later, which corresponds to a distance L,
ink droplets from adjoining nozzles in each of the nozzle groups
42, 44 are ejected almost simultaneously to form printed regions
48B, 48D. At this time, at boundary portions 49A, 49B, 49C between
the first-printed regions. 48A, 48C and the second-printed regions
48B, 48D, lines of different densities from other areas (in the
figure, dark lines with higher optical densities than those of
other areas) may be formed, significantly degrading the quality of
image. In the following description, a line of different density
than that of the surrounding area which shows at a boundary portion
between adjacent image regions printed by different nozzle groups
is referred to as a "joint line."
[0053] An elongate print head having all nozzles arrayed nearly in
a line does not produce such joint lines as are formed by the print
head of the above construction, and thus can perform a high quality
printing. However, forming such an elongate print head with a
single line of nozzles at a high nozzle density has many
difficulties in the process of manufacture and will increase the
manufacturing cost.
[0054] To deal with the above problem, it has been proposed and
implemented to arrange relative short nozzle groups in left and
right arrays alternately in a staggered manner to fabricate an
elongate print head easily at low cost. That is, an elongate print
head is manufactured by forming a plurality of short nozzle arrays
that can be manufactured at relatively low cost using the known
technology and arranging them in a staggered manner. With this
method nozzles can be located at precise positions more easily than
the method that arranges individually fabricated nozzle arrays in a
single line and bond them to a substrate. The proposed method is
also advantageous in terms of cost. FIG. 6 shows one such
example.
[0055] A print head 50 shown in FIG. 6 is an elongate print head
for a full-line type ink jet printing apparatus, which is made by
forming each nozzle group as an integral, fixed structure and
arranging these nozzle groups in a staggered manner. In the
following, X represents a direction in which a print medium is
transported relative to the print head and Y represents a direction
perpendicular to the print medium transport direction X.
[0056] Further, the X direction is also called a print head/medium
relative direction of motion, considering a case where the print
medium is transported in one pass in one direction relative to the
fixed full-line type ink jet print head during printing and also a
case where the print medium is intermittently transported relative
to the ink jet print head that is serially moved during the
printing operation.
[0057] In this print head 50, two nozzle arrays 51A, 51B each
having nozzles arrayed at equal pitches in the Y direction are laid
upstream and downstream with respect to the X direction. These two
nozzle arrays 51A, 51B form one nozzle group 51. The nozzles in the
downstream nozzle array 51B are situated intermediate in the Y
direction between the nozzles of the upstream nozzle array 51A.
Thus, in one nozzle group, the upstream nozzles and the downstream
nozzles adjoin each other in the Y direction, the nozzle array
direction, and are staggered by a distance of 5C. In other words,
the two nozzle arrays in one nozzle group form a staggered line of
nozzles. This arrangement provides a print head with a high nozzle
density in the Y direction, practically as high a nozzle density as
if the nozzles were arrayed in a straight line at a pitch of
5C.
[0058] The print head 50 shown here has a total of four nozzle
groups 51, 52, 53, 54 of the same construction as the nozzle group
51, arranged alternately on the upstream and downstream side with
respect to the X direction so that they are connected staggered in
the Y direction. The nozzles groups 51 and 53 assume the same
position in the X direction and the nozzle groups 52 and 54 are
also situated in the same position in the X direction.
[0059] Here, L1, L2 and L3 represent distances between nozzle
arrays in the X direction. L1 represents a distance between the
upstream nozzle arrays 51A, 53A of the upstream nozzle groups 51,
53 and the upstream nozzle arrays 52A, 54A of the downstream nozzle
groups 52, 54; L2 represents a distance between the upstream nozzle
array and the downstream nozzle array in each nozzle group; and L3
represents a distance between the downstream nozzle arrays 51B, 53B
of the upstream nozzle groups 51, 53 and the upstream nozzle arrays
52A, 54A of the downstream nozzle groups 52, 54 (also referred to
as a nozzle group distance).
[0060] In the print head 50 of the above construction, the distance
L2 between the upstream and downstream nozzle arrays in each nozzle
group and the distance L3 between the upstream and downstream
nozzle groups differ greatly. Thus, of the dots that have landed on
a print medium, those on boundary portions between image regions
printed by adjoining nozzle groups have different dot densities
than those of the surrounding areas, producing lines of density
variations over the entire image, degrading the image quality. This
is considered due to the following reasons.
[0061] When a printing operation is performed by the elongate print
head 50, two adjoining dots formed on a print medium by ink
droplets ejected from nozzles adjoining in the Y direction (simply
referred to as adjoining nozzles) overlap at their connected ends
to form a merged dot. This process is shown in FIGS. 13A, 13B and
13C.
[0062] The merged dot assumes either a gourd-like shape as shown in
FIG. 13A and FIG. 13B or an oval shape as shown in FIG. 13C.
[0063] FIG. 13A shows a merged dot formed by two adjoining dots
that landed on the print medium with a relatively large time
difference. An optical density of the overlapping portion of the
gourd-shaped, merged dot is apparently higher than other portions.
FIG. 13B shows a merged dot formed by two adjoining dots that
landed with a shorter time difference than that of FIG. 13A. There
is almost no difference in optical density between the overlapping
portion of the two dots and other portions. FIG. 13C shows a merged
dot formed by two adjoining dots that landed with an even shorter
time difference than those of FIG. 13A and FIG. 13B. Upon landing,
the ink of the two dots mixes to form an oval merged dot, rather
than the gourd-shaped dot.
[0064] As described above, the optical density and shape of a
merged dot formed on a print medium vary depending on the landing
time difference between the adjoining dots that form the merged
dot. When such a merged dot is formed continuously in the X
direction in one image, a density difference appears as a white or
black line (joint line), though its level of conspicuousness
depends on variations in ink dot landing position. In other words,
when the dots ejected from the nozzles in the boundary portion and
the dots ejected from the nozzles in the non-boundary portion are
all formed by one kind of the merged dot among the merged dots
shown in FIGS. 13A, 13B and 13C in Y direction, the density
difference (joint line) as mentioned above will not appear in X
direction.
[0065] In the above print head 50, droplets ejected from the
adjoining nozzles in each nozzle group land on a print medium with
a relatively short time difference that corresponds to the distance
L2. Thus, merged dots such as shown in FIG. 13B or FIG. 13C are
formed. In a boundary portion between adjoining nozzle groups,
however, droplets ejected from the adjoining nozzles land with a
relatively large time difference, thus forming merged dots as shown
in FIG. 13A. As a result, the boundary portion between adjacent
image regions has a different optical density than the surrounding
area. This density difference shows up as a line.
[0066] As still another related technology, a print head 60 shown
in FIG. 7 has been proposed. This print head 60 has two elongate
head units 61, 62 arranged in upstream and downstream positions
with respect to the X direction. In each of the elongate head units
61, 62, four nozzle arrays, each having nozzles arrayed in line in
the Y direction, are shifted to upstream and downstream sides
alternately and connected at their ends in the Y direction. The
nozzles in the downstream elongate head unit 62 are staggered in
the Y direction from the nozzles in the upstream elongate head unit
61 by a distance 6C, one-half the arrangement pitch of the nozzles
in each nozzle array. Thus, when viewed as a whole, the print head
60 has its nozzles arrayed in the Y direction at intervals of 6C,
which provides virtually the same nozzle density as if the nozzles
were formed in a single line at the arrangement pitch of 6C.
[0067] The print head 60 of the above construction also has the
similar problem described earlier. In the boundary portions E61,
E62, E63 between the adjoining nozzle arrays, the distances between
the adjoining nozzles in the Y direction differ from those of other
nozzles. Therefore, merged dots formed by these adjoining nozzles
have optical densities different from those of other merged dots,
resulting in a joint line. That is, in the boundary portion E61, a
lowermost nozzle (at a Y2-side end in the Y direction) of the
nozzle array 62B ejects an ink droplet forming a dot. A short
period of time later which corresponds to the distance L2, a nozzle
at the Y1-side end of the nozzle array 61B ejects an ink droplet
forming another dot. Then, a short time later which corresponds to
the distance L3, a nozzle at the Y2-side end of the nozzle array
62A ejects an ink droplet forming another dot.
[0068] After this, a short time later which corresponds to the
distance L2, a nozzle at the Y1-side end of the nozzle array 62B
ejects an ink droplet forming still another dot.
[0069] As described above, when merged dots are formed by the
nozzles in the boundary portion E61 between the adjoining nozzle
arrays, there is a slight difference between the time interval
corresponding to the distance L1 and the time interval
corresponding to the distance L3. Therefore, an overlapping portion
of a merged dot, which is formed by a dot ejected from the nozzle
at the Y2-side end of the nozzle array 62A and by a dot ejected
from the nozzle at the Y1-side end of the nozzle array 61B, has a
lower optical density than the overlapping portions of other merged
dots. If this merged dot is formed successively in the X direction,
a line of different density (joint line) extending in the X
direction shows. It is known that the landing positions of ink dots
ejected from end nozzles of each nozzle array are easily disturbed.
This increases a possibility that an ink dot from the Y2-side end
nozzle of the nozzle array 61A and an ink dot from the Y1-side end
nozzle of the nozzle array 61B may merge together, making the
formation of another joint line likely. These density variations
similarly occur also in other boundary portions E62, E63.
[0070] A further related technology, such as shown in FIG. 8, has
been proposed.
[0071] A print head 70 shown here has two elongate head units
arranged in parallel, each having four nozzle arrays arrayed in a
staggered manner and connected at their ends, as with the print
head 60 of FIG. 7. In this related technology, however, an upstream
elongate head unit 71 has upstream nozzle arrays 71A, 71C and
downstream nozzle arrays 71B, 71D separated a large enough distance
in the X direction. Similarly, a downstream elongate head unit 72
has upstream nozzle arrays 72A, 72C and downstream nozzle arrays
72B, 72D separated a large enough distance in the X direction. With
this arrangement, the nozzles in any of the border portions E71,
E72, E73 between the adjoining nozzle arrays form adjoining dots in
such a way that they overlap after the preceding dots have been
fixed well. Thus, the merged dots are all formed as shown in FIG.
13A, producing a relatively good image. With this print head 70,
however, the arrangement of signal lines is complicated for the
reason described above and the head width in the X direction
becomes large, increasing the size of the printing apparatus.
First Embodiment of this Invention
[0072] To solve these problems experienced with the related
technologies described above, the first embodiment of this
invention provides a print head constructed as shown in FIG. 9 for
use in the full-line type ink jet printing apparatus of FIG. 1.
[0073] In FIG. 9, reference numbers 81, 82, 83, 84 represent nozzle
groups each made up of an odd-numbered nozzle array and an
even-numbered nozzle array. These nozzle groups are alternately
shifted to different positions in the X direction, i.e., to
upstream and downstream side, and connected at their ends in the Y
direction, thus forming an elongate print head 80 extending in the
Y direction. Of these nozzle groups, the nozzle groups 81, 83 are
situated in the same upstream position with respect to the X
direction and the nozzle groups 82, 84 are likewise situated in the
same downstream position with respect to the X direction. While in
FIG. 9 the elongate print head 80 is shown to have four nozzle
groups 81-84, it is possible to arrange three nozzle groups or four
or more nozzle groups in one print head.
[0074] These nozzle groups have the same construction. For example,
the nozzle group 81 has an odd-numbered nozzle array 81A and an
even-numbered nozzle array 81B. The odd-numbered nozzle array 81A
is made up of those of nozzles n arrayed at a predetermined pitch
in the Y direction which are situated in odd-numbered positions
from the upper end of the nozzle array; and the even-numbered
nozzle array 81B is made up of those of the nozzles n which are
situated in even-numbered positions from the upper end of the
nozzle array (including a 0th position). The nozzles of the
even-numbered nozzle array 81B are so arranged as to be situated
intermediate in the Y direction between the nozzles of the
odd-numbered nozzle array 81A. Thus, in one nozzle group, the
nozzles in the odd-numbered nozzle array and the nozzles in the
even-numbered nozzle array are situated close to each other in the
Y direction in which the nozzles are arrayed, and their pitch is
8C. Thus, in this nozzle group 81 the nozzles n are arranged
staggered in two nozzle arrays 81A, 81B, forming a high-density
nozzle head. In other words, this construction can provide
virtually the same nozzle density as if the nozzles were arrayed in
a single line at the pitch of 8C. The nozzle arrays 81A, 81B are
each formed in separate substrates, both of which are integrally
supported by a support plate P.
[0075] L1, L2, L3 represent distances in the X direction between
the nozzle arrays. L1 represents a distance between the
odd-numbered nozzle arrays 81A, 83A in the upstream nozzle groups
81, 83 and the odd-numbered nozzle arrays 82A, 84A in the
downstream nozzle groups 82, 84. L2 represents a distance between
the odd-numbered nozzle array and the even-numbered nozzle array in
each nozzle group. L3 represents a distance between the
even-numbered nozzle arrays 81B, 83B in the upstream nozzle groups
81, 83 and the odd-numbered nozzle arrays 82A, 84A in the
downstream nozzle groups 82, 84 (also referred to as a nozzle group
distance). In FIG. 9, E81, E82 and E83 indicate boundary portions
between the nozzle groups.
[0076] When printing a solid image using the print head 80
described above, in the boundary portion E81 between the nozzle
groups, a nozzle at the Y2-side end in the Y direction of the
nozzle array 81A first ejects an ink droplet. This is followed by a
nozzle at the Y2-side end of the nozzle array 81B, by a nozzle at
the Y1-side end of the nozzle array 82A and then by a nozzle at the
Y1-side end of the nozzle array 82B in that order. Dots are formed
by the ink droplets ejected from these nozzles successively.
[0077] The landing time difference between adjoining dots formed by
the adjoining nozzles in each nozzle group 81, 82 matches the
distance L2. This time difference is so set that two adjoining dots
partly overlap each other to form a gourd-shaped merged dot, such
as shown in FIG. 13A or FIG. 13B. In the boundary portion E81
between the nozzle groups 81 and 82, a nozzle at the Y1-side end of
the nozzle array 82A and a nozzle at the Y2-side end of the nozzle
array 81B are adjacent each other in the X direction and their ink
droplet landing positions have the following relationship. A dot
formed by an ink droplet ejected from a nozzle at the Y2-side end
in the Y direction of the nozzle array 81B and a dot formed by an
ink droplet ejected from a nozzle at the Y1-side end of the nozzle
array 82A partly overlap each other to form a merged dot. The
landing time difference between these two dots correspond to the
distance L3. This distance L3 is set almost equal to the distance
L2 when a print medium is moved at a constant speed through a
position facing the print head that is performing a printing
operation. So, the merged dot formed by the nozzles in the boundary
portion E81 as well as the merged dot formed by being ejected from
the nozzles in nozzle arrays 81A and 81B, the nozzle arrays being
spaced apart to each other by a distance L2, are formed in
gourd-like shape as shown in FIG. 13A or 13B.
[0078] What is meant by the expression "almost equal" is as
follows. In a configuration where printing is performed in one pass
of a print medium relative to the print head, the distance is
"almost equal" to the distance to such an extent that the merged
dot formed by ink drops, ejected from two nozzles both in one
nozzle group or one in each of two adjacent nozzle groups and close
to each other in the relative movement direction of the print
medium and the print head (X direction), is formed with same shape
and density.
[0079] Therefore, the merged dots formed by the nozzles in the
boundary portion E81 and the merged dots formed by the nozzles in
each of the nozzle groups 81, 82 are almost equal in shape and
optical density in their overlapping portion. As a result, no
density variation-caused lines are formed and a satisfactory image
quality can be obtained.
[0080] The nozzle groups may be arranged so that they overlap at
their ends. In the boundary portion E82 between the nozzle groups
82 and 83, the nozzle arrays of the two groups partly overlap in
the Y direction. That is, in the boundary portion E82, a few
nozzles at the lower end portion of the nozzle array 82A and a few
nozzles at the upper portion of the nozzle array 83A occupy the
same positions in the Y direction. A few nozzles at the lower end
portion of the nozzle array 82B and a few nozzles at the upper end
portion of the nozzle array 83B occupy the same positions in the Y
direction.
[0081] In this boundary portion E82, a nozzle at the Y1-side end in
the Y direction of the nozzle array 83A first ejects an ink
droplet, followed by a nozzle at the Y1-side end of the nozzle
array 83B, followed by a nozzle at the Y2-side end in the Y
direction of the nozzle array 82A and then by a nozzle at the Y2
side end in the Y direction of the nozzle array 82B in that order
so that dots formed by these nozzles are successively formed to
overlap each other in the Y direction. In this process, of the
nozzles at the Y2-side end in the Y direction of the nozzle arrays
82A, 82B, those overlapping the Y1-side end in the Y direction of
the nozzle arrays 83A, 83B include active or enabled nozzles (used
for ejection) and inactive or disabled nozzles (not used for
ejection). Desired active nozzles can be selected from these
overlapping nozzles. That is, the nozzle selection is made such
that the nozzles selected in the boundary portion E82 to form four
dots adjoin at a pitch of 8C in the Y direction and that no two ink
droplets land at the same position for one dot. This nozzle
selection enables the landing time differences between the four ink
droplets ejected from the selected nozzles in the boundary portion
E82 to match the distances L2 and L3, thus eliminating the density
variation-caused lines.
[0082] Likewise, in the boundary portion E83 too, the density
variation can be prevented as in the boundary portion E81.
[0083] As described above, the elongate print head 80 according to
the first embodiment makes it possible to form an image at high
speed and reliably prevent the formation of density
variation-caused lines in the image. Further, since the elongate
print head of the first embodiment is constructed by arranging
short nozzle groups in a staggered pattern, it can be manufactured
easily at low cost.
Second Embodiment of this Invention
[0084] Next, a second embodiment of this invention will be
explained by referring to FIG. 10.
[0085] A print head 90 in the second embodiment is an elongate
print head which, as in the first embodiment, has a plurality of
nozzle groups of the same construction (four nozzle groups 91, 92,
93, 94) arranged staggered. It is noted, however, that two nozzle
arrays making up each nozzle group differ from those of the first
embodiment.
[0086] Let us take a nozzle group 91 for example. Nozzle arrays
91A, 91B in the nozzle group 91 each have their nozzles arranged
staggered.
[0087] The nozzle array 91A has nozzle array forming elements 91A1,
91A2 arrayed in a staggered manner along two parallel limes a small
distance L4 apart in the X direction. Like the nozzle array 91A,
the nozzle array 91B has two lines of nozzle array forming elements
91B1, 91B2 and is arranged parallel to the nozzle array 91A. In
each of these nozzle arrays the nozzles are arranged at a pitch of
9B. Further, the nozzles in the nozzle array 91B are situated
intermediate between the nozzles of the other nozzle array 91A.
Therefore, when viewed as a whole, the nozzle group 91 has a nozzle
pitch of 9C (=9B.times.1/2) in the Y direction. Other nozzle groups
have the similar construction.
[0088] The nozzle array forming elements in the nozzle group 91 and
the nozzle array forming elements in the nozzle group 93 are
arrayed in the same straight lines running in the Y direction; and
the nozzle array forming elements in the nozzle group 92 and the
nozzle array forming elements in the nozzle group 94 are also
arrayed in the same straight lines running in the Y direction.
[0089] In FIG. 10, L1 denotes a distance in the X direction between
the upstream side nozzle array forming elements 91A1, 93A1 in the
nozzle groups 91, 93 situated on the upstream side with respect to
the X direction and the upstream side nozzle array forming elements
92A1, 94A1 in the downstream side nozzle groups 92, 94. L2 denotes
a distance in the X direction between adjoining nozzles in each
nozzle group. L3 denotes a distance in the X direction between the
downstream side nozzle array forming elements 91B2, 93B2 of the
upstream side nozzle groups 91. 93 and the upstream side nozzle
array forming elements 92A1, 94A1 of the downstream side nozzle
groups 92, 94 (also referred to as a nozzle group distance in the X
direction). The distances L2 and L3 are set almost equal.
[0090] In a boundary portion E91 between the nozzle group 91 and
the nozzle group 92, nozzles n1, n2, n3, n4 situated at the lower
end of the nozzle array forming elements 91A1, 91B1, 91A2, 91B2 are
set close to each other successively in that order in the Y
direction. Immediately below the nozzle n4 at the lower end of the
nozzle array forming element 91B2 are nozzles n5, n6, n7, n8 that
are situated at the upper end of the nozzle array forming elements
92A1, 92B1, 92A2, 92B2 and are set close to each other successively
in that order in the Y direction. These eight nozzles successively
eject ink droplets to form dots, with the adjoining dots partly
overlapping to form merged dots.
[0091] Distances in the X direction between adjoining nozzles in
the same nozzle group are all L2 and thus landing time difference
between the adjoining nozzles are uniform Thus, the merged dots
formed by the adjoining nozzles are gourd-shaped, as shown in FIG.
13A or FIG. 13B. The distance between the nozzle n4 at the lower
end of the nozzle array forming element 91B2 and the nozzle n5 at
the upper end of the nozzle array forming element 92A1 is L3. This
distance L3 is set nearly equal to the distance L2. Therefore, the
landing time difference between the ink droplets ejected from the
adjoining nozzles n4 and n5 is nearly equal to the landing time
difference between ink droplets ejected from other adjoining
nozzles.
[0092] As a result, the merged dots formed by ink droplets ejected
from the nozzles n1-n8 are all gourd-shaped, as shown in FIG. 13A
or FIG. 13B, and the optical density of an overlapping portion in
each gourd-shaped merged dot is uniform. Therefore no density
variation-caused lines are formed in a printed image.
[0093] The overlapping configuration like the one described above
may also be adopted. For example, in the boundary portion E92, a
few nozzles at the Y1-side end portion of the nozzle array forming
elements 93A1, 93A2, 93B1, 93B2 and a few nozzles at the Y2-side
end portion of the nozzle array forming elements 92A1, 92A2, 92B1,
92B2 partly overlap in the Y direction. Among these nozzles in the
boundary portion E92 a nozzle selection is made such that the
nozzles selected to form eight dots adjoin at a pitch of 9C in the
Y direction and that no two ink droplets land at the same position
for one dot. This nozzle selection enables the landing time
differences between the eight ink droplets ejected from the
selected nozzles in the boundary portion E92 to match the almost
equal distances L2 and L3, thus eliminating the density
variation-caused lines.
[0094] Also in the boundary portion E93, as in the boundary portion
E91, density variations can be prevented. Where a high-density
nozzle arrangement is used as in this embodiment, the volume of ink
ejected from each nozzle during the printing operation is smaller
than when the adjoining nozzles are arranged at a larger pitch.
More precisely, the ink ejection volume is determined so that a dot
formed has a diameter of about {square root}2.times.nozzle
pitch.
Third Embodiment of this Invention
[0095] FIG. 11 shows a third embodiment of this invention. A print
head 100 shown here has two sets of those nozzle groups used in the
first embodiment of FIG. 9 arranged side by side in the X
direction. With this arrangement, the similar effect to that of the
above embodiments can be expected and adjoining dots stably form
merged dots of the shape of FIG. 13A.
Fourth Embodiment of this Invention
[0096] FIG. 12 shows a fourth embodiment of this invention. In a
print head 110 shown here, each of nozzle groups comprises a single
array of nozzles. These nozzle arrays are arranged in pairs so that
two in each pair oppose each other in the X direction with a
distance L2 in between. The paired nozzle arrays are so set that
the nozzles in one array and the nozzles in the other are staggered
in the Y direction by a pitch 11C. Further, these nozzle pairs are
arranged staggered between two parallel lines extending in the Y
direction in such a way that the paired nozzle arrays situated on
the upstream side with respect to the X direction and the paired
nozzle arrays situated on the downstream side partly overlap at
their upper and lower ends in the Y direction.
[0097] In this embodiment also, since the adjoining nozzles
successively form adjoining dots at time intervals corresponding to
the almost equal distances L2 and L3, merged dots formed by these
adjoining dots have a uniform optical density which in turn leads
to a high quality image.
Other Embodiments
[0098] While in the above embodiments a full-line type print head
has been taken up as an example, this invention is also applicable
to a so-called serial type ink Jet printing apparatus which moves a
print head in a direction crossing the print medium transport
direction as the print head prints on the print medium. In that
case, this invention is effective not only for a one-pass printing,
which completes the printing in any one image area in one printing
scan (pass), but also for a multi-pass printing, which completes
the printing in any one image area in a plurality of printing
scans.
[0099] In the above embodiments, an ink jet printing apparatus has
been described which uses a print head ejecting ink droplets of a
constant ink volume. This invention is also applicable to a print
head having nozzles capable of ejecting ink droplets of different
ink volumes. Further, this invention can also be applied to a print
head which, in addition to yellow, cyan, magenta and black inks,
ejects light or dark inks of the same colors with different
densities.
[0100] This invention is particularly advantageous when applied to
a printing apparatus that uses an ink jet print head which utilizes
thermal energy in ejecting ink from nozzles as flying ink droplets
for printing.
[0101] The serial type ink jet printing apparatus are available in
a variety of configurations. For example, in one configuration, the
print head is secured to the printing apparatus body; in another
configuration a replaceable chip type print head is replaceably
mounted on the printing apparatus body for electrical connection
with and for ink supply from the apparatus body; and in still
another configuration a cartridge type print head is integrally
attached with an ink tank. This invention is effectively applied to
any of these configurations.
EXAMPLE PRINTING OPERATIONS
[0102] This invention will be explained in more detail in example
printing operations.
EXAMPLE OPERATION 1
[0103] In this example, a printing operation was performed by using
the elongate print head 80 of FIG. 9 as the ink jet print head of
FIG. 1 in this elongate print head 80, an upstream nozzle array and
a downstream nozzle array making up each nozzle group were
constructed to have a nozzle density of 600 dpi. More specifically,
head chips of on-the-shelf BJF850 cartridges (Canon make) were
combined and only those nozzle groups arranged as shown in FIG. 9
were used to construct an elongate print head. Thus, each nozzle
group has 256 nozzles arranged at a pitch of 1200 dpi. Four of the
nozzle groups of the above construction were shifted alternately to
the upstream side and to the downstream side for a staggered
arrangement.
[0104] This elongate print head was used on an ink jet printing
apparatus to eject ink droplets containing a predetermined colorant
to form dots on a print medium. The ink was ejected in droplets
each 4.5.+-.0.5 pl in volume. Ink dedicated for BJF850 cartridge
(Canon make) was used as the ink containing a colorant.
[0105] Photo-glossy paper dedicated for ink jet (Pro-photo paper,
PR101: Canon make) was prepared as a print medium.
[0106] An ejection drive frequency at which ink droplets were
ejected from the print head nozzles was set at 8 kHz.
[0107] Image data was printed in one printing scan of the elongate
print head 80. No optical density difference was observed between
an image printed by those nozzles in the boundary portion between
the staggered nozzle groups and an image printed by other nozzles,
and an image produced was uniform in density.
EXAMPLE OPERATION 2
[0108] Four of the above elongate print heads were used to print a
pattern of grayscale steps as a full-color image with a maximum ink
volume of 200% (up to two 4.5-pl ink dots were used for each pixel
in a print matrix of 1200 dpi). As with the example operation 1, no
density difference was observed between an image printed by those
nozzles in the boundary portion of different nozzle groups and an
image printed by other nozzles.
EXAMPLE OPERATION FOR COMPARISON
[0109] In place of the elongate print head used in the example
operation 1, an elongate print head shown in FIG. 5A was used in
one-pass printing. In this printing, an image printed by those
nozzles in the boundary portion of different nozzle groups was
found to have density variation-caused lines and its quality was
degraded.
[0110] As described above, these example operations can thoroughly
eliminate the conventional problems experienced during the printing
operation using an elongate print head that is made by combining
nozzle groups of relatively short nozzle arrays. That is, merged
dots formed by ink droplets ejected from adjoining nozzles in the
boundary portions between the, nozzle groups can be made equal in
optical density to merged dots formed by adjoining nozzles in an
interior of each nozzle group. This in turn prevents the formation
of density variation-caused lines, assuring a good quality
image.
[0111] Further, arranging both the nozzle arrays and the nozzle
groups in a staggered configuration can not only array nozzles in
the print head at high density but also locate the nozzles in each
nozzle group at more precise positions than when longer nozzle
groups are individually arranged on a substrate. This staggered
arrangement also makes the wiring of signal lines connecting to the
nozzle groups easy and therefore minimizes an increase in the size
of the print head in the width direction of the print medium.
Further, this arrangement renders the manufacture of the print head
extremely easy when compared with a configuration in which nozzles
are highly densely arrayed in a single array, significantly
reducing the manufacturing cost.
[0112] The present invention has been described in detail with
respect to preferred embodiments, and it will now be apparent from
the foregoing to those skilled in the art that changes and
modifications may be made without departing from the invention in
its broader aspect, and it is the intention, therefore, in the
apparent claims to cover all such changes and modifications as fall
within the true spirit of the invention.
[0113] This application claims priority from Japanese Patent
Application Nos. 2003-417361 filed Dec. 15, 2003 and 2004-308822
filed Oct. 22, 2004, which are hereby incorporated by reference
herein.
* * * * *